1. Field of the Invention
The present invention relates generally to a sealing unit for sealing the end of a blank tube and, more particularly, to a sealing unit for sealing the end of a tube in a hydroforming station.
2. Description of the Related Art
Industry requires standard tubular blanks to be formed into one-piece, complex tubular shapes. In the automobile industry, automobile frames are typically of the xe2x80x9cboxxe2x80x9d type construction for strength and load bearing purposes. These frame members often have a great variation in both the horizontal and vertical profile. The cross-section of such members often varies rather extremely from approximately a square cross-section, to a rectangular cross-section to a round cross-section to a severely flattened cross-section, and to any irregularly shaped combination of the above. The same is true for the antenna industry, which requires a wide variety of cross-section shapes for waveguides.
An apparatus that forms the desired one-piece, complex tubular shapes from tubular blanks is a hydroforming station or hydroforming press. The hydroforming station follows a series of steps to form the desired tubular shape. First, a blank tube or workpiece is placed between a pair of dies having cavities defining the desired resultant shape of the formed tube. The ends of the workpiece are tightly sealed with a pair of sealing units. The workpiece is filled with fluid which is then pressurized. Pressurizing the fluid within the workpiece results in forming and expanding the tube to conform to the cavity shape. The fluid is drained from the tube and the sealing units are removed to release the formed frame.
Conventional sealing units implement a flexible gasket, resilient elastomeric annular seal or O-ring. Typically, the O-ring relies on contact with the external surface of the tube to maintain a fluid seal. In some applications, especially low pressure hydroforming below 5000 pounds per square inch, the conventional O-ring sealing unit may perform adequately. However, at higher hydroformning pressures above 5000 pounds per square inch, the conventional O-ring sealing units do not perform adequately. Even at the low pressure hydroforming, the O-ring sealing unit has some shortcomings. The main shortcoming of the conventional sealing unit is that it tends to be the first part of the hydroforming press to fail. Because workpieces are unfinished, they often have burrs on the edges of their openings. The repetitive motion of the O-ring over these burrs on multiple workpieces damage the O-rings. Additionally, constant friction between the O-ring and workpieces wear down the gasket material. Repeated use of the sealing units results in the necessity of frequent replacement of the O-rings. Constant replacement of the O-rings results in large maintenance costs and large inefficient down times.
For the hydroforming station to properly function, the sealing units must maintain a tight fluid seal. For high pressure hydroforming, the O-ring sealing units, especially worn O-rings, may fail to maintain a tight fluid seal. Failure of the O-ring in conventional sealing units results in leaking and non-functioning hydroforming press. Even worse, an O-ring failure could result in great harm to machine operators or adjacent machinery. The release of the highly pressurized fluid could result in death and destruction. Conventional hydroforming presses with their O-ring implementing sealing units require some form of machine guard or personal protection. These additional safety precautions resulting in added costs and obstructed views.
The present invention is directed to overcoming or at least reducing the effects of, one or more of the problems set forth above.
In accordance with one aspect of the present invention, there is provided a sealing unit capable of sealing engagement with an end of a tube. The seal unit comprises a tapered element, a sealing ring and a base. The tapered element having a longitudinal axis is adapted for insertion into a bore in the end of the tube. The sealing ring is co-axial with the longitudinal axis of the tapered element providing an annular channel between the tapered element and the sealing ring. The annular channel is capable of receiving the end of the tube. The base, being co-axial with the longitudinal axis of the tapered element, contacts the sealing ring holding it in place. The base also contacts the tapered element terminating the annular channel. When the sealing unit sealably engages the end of the tube, the tapered element sealably engages the inner wall of the tube, and the sealing ring sealably engages the outer wall of the tube.
In accordance with another aspect of the present invention, there is provided a sealing unit capable of sealing engagement with an end of a tube. The sealing unit further comprises a housing and at least one stop element. The base has a front end and a back end. Proximate to the back end of the base is the housing, and the housing is connected to the tapered element. The stop element is positioned between the housing and the sealing base. When the end of the tube is positioned within the annular channel, and the base is stationary relative to the tube, the housing is capable of sliding toward said back end of said stationary base compressing the stop element. The tapered element, being connected to the housing, is capable of sliding further into the bore until the tapered element sealably engages the inner wall of the tube. When the tapered element is in sealable engagement with the inner wall of the tube, the tapered element forces the inner wall of the tube outward providing sealable engagement between the outer wall of the tube and the sealing ring.
In accordance with a further aspect of the present invention, there is provided a sealing unit capable movement between a sealed position and a retracted position. The sealing unit comprises a sealing unit moving means capable of moving the sealing unit between the retracted position and the sealed position. The sealing unit moving means is connected to the housing. In the retracted position, the sealing unit is positioned away from the end of the tube. In the sealed position, the sealing unit sealably engages the end of the tube.